Hydraulically actuated reciprocating downhole pumps are known to those skilled in the art as exemplified by the following George K. Roeder U.S. Pat. Nos. 4,084,923; 4,477,234; 4,768,589; and 3,957,400, for example only. The simplest of the downhole hydraulically actuated pumps involve a number of moving parts and are quite complex in operation. It is known to circulate the entire hydraulically actuated pump uphole and downhole in order to effect repairs thereon, or in order to replace one pump with another pump. Those skilled in the art are also familar with jet pumps that can be used in lieu of a reciprocating type hydraulically actuated downhole pump as evidenced by the Roeder U.S. Pat. Nos. 4,744,730; 4,293,283; and 4,183,722.
It is also old to combine a jet pump with a reciprocating type hydraulically actuated downhole pump as evidenced by the Roeder U.S. Pat. No. 4,202,656. It is also old to circulate the entire jet pump into and out of the borehole as evidenced by the Roeder U.S. Pat. Nos. 4,744,730 and 4,183,722. Sometimes to facilitate circulating the pump in and out of a hole, the packer nose assembly shown in Roeder U.S. Pat. No. 4,248,299 is advantageously employed.
There are many hydrocarbon producing slim hole wells that produce both gas and liquid, wherein the information gas pressure and volume is insufficient to lift the formation liquid to the surface, and these wells must therefore employ some sort of lifting device. These wells sometime will produce both gas and liquid for several hours and eventually become "loaded" as the well hydrostatic head overcomes the lifting action of the downhole gas pressure and the well is "killed" or "shuts itself in". When this happens, the well will remain shut-in until the downhole pressure builds up to a value that once again overcomes the hydrostatic head, whereupon the well will again flow and produce both gas and oil until the reflux action of the liquid presents a hydrostatic head that overcomes the available downhole gas pressure. This causes the well to again shut itself in. In instances such as this, an inexpensive downhole jet pump can be advantageously used to assure that the well is continuously produced, as contrasted to the well being shut-in at odd intervals of time. There are many advantages derived from continuously producing such a well as contrasted with shutting the well in until the downhole pressure has recuperated.
In a production well such as described, it is possible to recirculate the produced gas back downhole to the jet pump in order to lift the formation fluid with a jet action and thereby further enhance the production rate by utilizing the reinjected gas along with the produced gas as a sort of gas lift. This is considered part of the present invention.
It is old to place check valves within a packer nose assembly in order to circulate the entire pump assembly into and out of a borehole as evidenced by the following Roeder U.S. Pat. Nos. 4,293,283; 4,268,227; 4,214,854; 4,202,656; 4,118,154; 4,084,923 and 4,080,111.
Roeder U.S. Pat. No. 4,744,730 shows a jet pump of both the free and the fixed type.
The present invention provides a downhole jet pump that can be used for producing liquids as well as a mixture of liquid and gas; and provides improvements in the nozzle assembly and method and apparatus for which the nozzle assembly can be retrieved without pulling the pump from the borehole. This is especially advantageous in the fixed type downhole jet pump where the nozzle and throat is subjected to rapid wear, because it provides a great savings by avoiding the costly use of a pulling unit.
In this disclosure, the term fluid is intended to include gas, water, liquid hydrocarbons, and any other composition of matter that can be used as a power fluid and circulated downhole to operate a jet pump.